Objective: To develop a model for immunoprophylaxis and immunotherapy of lung cancer in Syrian golden hamsters using viable and nonviable preparations of Mycobacterium bovis (Strain BCG). Approach: Hamsters are treated with 10 intratracheal instillations of benzo(a)pyrene. At various times either before, during or after carcinogenesis, animals are infected with BCG and effects on the latent period and incidence of benzo(a)pyrene induced bronchogenic carcinoma are evaluated. The immunobiology of syngeneic lung tumors are being studied for the purpose of establishing a model for immunotherapy of lung metastasis. Companion studies will investigate the immunosuppressive effects of carcinogen and the role of BCG in counteracting the action of benzo(a)pyrene.